During the manufacture of semiconductor devices such as a memory devices, logic devices, and microprocessors, various processes are commonly performed. Etching silicon nitride selective to silicon (such as polysilicon) and to silicon dioxide with various etch ratios is often required. For example, hot phosphoric acid isotropically etches silicon nitride selective to silicon dioxide and silicon. Other processes for etching Si3N4 selective to SiO2 and Si are discussed in “Highly Selective Etching of Silicon Nitride Over Silicon and Silicon Dioxide,” J. Vac. Sci. Technol. A 17(6), November/December 1999, which describes the use of oxygen (O2) and nitrogen (N2) in combination with CF4 or NF3. The processes discussed achieve Si3N4 to Si and to SiO2 etch rate ratios of up to 100 and 70 respectively using nitrogen trifluoride. The processes use high flow rates of 800 standard cubic centimeters (sccm) O2 and 110 sccm N2 for most experiments. Further, using carbon tetrafluoride, a Si3N4 to polysilicon etch ratio of 40 was achieved while SiO2 was not etched at all. Etch rates of silicon nitride are below about 50 angstroms (Å) per minute.
As semiconductor manufacture typically requires high volume processing to lower costs, any decrease in temporal processing requirements can result in a large increase in product throughput. Further, having options available to accomplish a task such as etching silicon nitride is advantageous, as one process may function better for certain manufacturing flows. Additional methods for etching silicon nitride selective to silicon and silicon nitride at an accelerated rate would be desirable.